The invention relates to solvents for agents in the form of neutralizing media that efficiently mass deacidify books, printed matter and other paper products, as well as archived materials of all sorts, such as newspapers, records and documents.
All printed matter and paper products, in particular books, are subject to aging of the paper during storage, during the course of which traces of acid are released, leading to progressive damage to the paper.
If countermeasures are not undertaken, after a number of decades this damage can lead to the complete disintegration of the paper.
In order to preserve archives and libraries holding several hundred million books worldwide it is therefore necessary that the acid in the paper be neutralized and to simultaneously incorporate a buffering substance in the paper in sufficient quantity to neutralize acids released in the paper in the future.
In view of the very large quantity of books, only those processes which permit the efficient mass treatment of a large quantity of books in their entirety can be considered for this purpose; that is, processes which do not require opening the binding of the book and treating individual pages.
According to a process which is already known, the books are treated with vapor of metal alkyls for the purpose of deacidification, e.g. with diethylzinc vapor (U.S. Pat. No. 3,969,549). Due to moisture in the paper, the metal alkyl is converted to the oxide of the metal, e.g. into zinc oxide, which remains in the paper, neutralizing the free acids.
This process can be viewed as a "dry" process; that is, the books only come in contact with the vapor of the metal alkyl and are not saturated with a liquid.
This process achieves good deacidification, while not damaging the books.
The metal alkyls that are suitable for this application are, however, substances that are self-igniting in air and pose an extreme danger of fire and explosion and require the greatest degree of care and expensive safety measures to avoid serious accidents.
According to another known process, the so-called Wei-T'o process, the books are treated with solutions of an organo-metallic compound such as, for example, methylmagnesium carbonate, in suitable solvents such as the solvents mentioned below.
Using the example of methylmagnesium carbonate, this in turn is converted into magnesium oxide and magnesium carbonate by moisture in the paper, and both of these are capable of neutralizing the acids in the paper.
In contrast to the initially mentioned "dry" process, in this process the books are saturated with a liquid.
In addition to the main objective already mentioned, that being the deacidification of books, this process furthermore rinses away dust and dirt particles, similar to chemically cleaning textiles. Herein, aside from this process being safe, a further significant advantage can be seen.
It is necessarily true that very high requirements are placed on the chemical-physical properties of the solvents that are used in order to treat the books without damage.
Various secondary materials in addition to paper were and will be used in the manufacture of books, such as, for example, glue, adhesives, inks, including printing inks, cardboard, cloth, leather, and synthetics.
The solvents employed in the deacidification must neither damage the paper nor the secondary materials used to manufacture the book in any manner whatsoever. Since the solvents used in a dry process are removed from the books following the deacidification, the solvents must vaporize at temperatures which cause no damage to the books.
Previously, such non-damaging substances as fluorohydrocarbons and chlorofluorohydrocarbons (CFHC) were used along with the addition of alcohols such as, e.g., methanol or ethanol.
The mentioned fluorohydrocarbons and chlorofluorohydrocarbons are sufficiently compatible with most book materials and vaporize at temperatures at which, on the one hand, no significant evaporative losses occur during handling while, on the other hand, the books are not damaged.
However, in particular for chlorofluorohydrocarbons, there are highly significant manufacturing and application limitations as a result of their high potential for causing environmental and ozone layer damage.
In consideration of these worldwide limitations and their intensification as already fixed into contracts, a worldwide ban on application is to be expected.
German patent application DE 39 04 111 Al however specifies a process for mass deacidification of books and paper products in an environmentally safe manner, whereby emissions can be avoided to a large extent by means of an enclosed procedure and by carefully purifying the exhaust air. But if the production of fluorohydrocarbons or chlorofluorohydrocarbons is no longer possible in the foreseeable future as a result of a ban and/or voluntary discontinuance, suitable solvents for this efficacious, operationally safe and efficient process will be lacking.
The invention is thus assigned the basic task providing new solvents which are suitable for mass deacidification of paper products and permit their deacidification with the least possible damage to the products, while avoiding substances that have environmental drawbacks.